A baby three-toed skink emerging from an egg. (Not part of the research). Photo: Nadav Pezaro, Haifa University

Which came first, the lizard or the egg?

Embargoed until: Publicly released:

In a world first, Sydney biologists have observed a three-toed skink lay eggs and give birth to a live baby from the same pregnancy, opening a useful pathway to study the evolution of pregnancy.

Journal/conference: Biology Letters

DOI: 10.1098/rsbl.2018.0827

Organisation/s: The University of Sydney

Media Release

From: The University of Sydney

In a world first, researchers at the University of Sydney have observed a normally live-bearing Australian lizard lay three eggs and then weeks later, give birth to a live baby from the same pregnancy. This is the first time such an event has been documented in a single litter of vertebrate babies.

The three-toed skink (Saiphos equalis) is one of only a handful of rare “bimodally reproductive” species, in which some individuals lay eggs and others give birth to live babies. But up until now, no vertebrate has ever been observed to do both in one litter.

“It is a very unusual discovery,” said Dr Camilla Whittington, from the School of Life and Environmental Sciences and Sydney School of Veterinary Science at the University of Sydney.

The three-toed skink is native to the east coast of Australia. In the northern highlands of New South Wales the animals normally give birth to live young, but those living in and around Sydney lay eggs.

“We were studying the genetics of these skinks when we noticed one of the live-bearing females lay three eggs,” Dr Whittington said. “Several weeks later she gave birth to another baby. Seeing that baby was a very exciting moment!”

The observation will be published in Biology Letters this week, along with advanced microscopy of the egg-coverings.

There are at least 150 evolutionary transitions from egg-laying to live-bearing in vertebrates said Dr Whittington, who led the study alongside Dr Melanie Laird, a postdoctoral researcher at the University of Otago, and Emeritus Professor Mike Thompson.

“The earliest vertebrates were egg-layers, but over thousands of years, developing embryos in some species were held inside the body for longer, until some animals began to give live birth. People mostly think about humans and other mammals giving birth. But there are many species of reptile that give birth, too.”

Dr Whittington said that the unusual observation of both egg laying and live birth in a single litter shows that the three-toed skink is an ideal model for understanding pregnancy. “It makes Australia one of the best places in the world to study the evolution of live birth, because we can watch evolution in action,” she said.

“Put in the context of evolutionary biology, being able to switch between laying eggs and giving live birth could allow animals to hedge their bets according to environmental conditions,” Dr Whittington said.

This observation helps make the three-toed skink, which looks like a baby snake with tiny legs, one of the “weirdest lizards in the world”, she said.

Further research into this small lizard, which seems to occupy a grey area between live birth and egg-laying, will help determine how and why species make major reproductive leaps.

The research paper is available upon request.

Attachments:

  • The University of Sydney
    Web page
    Download photos of Dr Camilla Whittington, a skink hatching and of a skink embryo at this link.
  • The University of Sydney
    Web page
    Download short videos of a three-toed skink eating crickets at this link.
  • The Royal Society
    Web page
    The URL will go live after the embargo ends.

News for:

Australia
VIC

Multimedia:

  • Dr Camilla Whittington
    Dr Camilla Whittington

    Dr Camilla Whittington from the School of Life and Environmental Sciences and Sydney Veterinary School at the University of Sydney.

    File size: 1.4 MB

    Attribution: L'Oreal

    Permission category: © - Only use with this story

    Last modified: 03 Apr 2019 10:20am

    NOTE: High resolution files can only be downloaded here by registered journalists who are logged in.

  • Dr Camilla Whittington holding a Cunningham's skink.
    Dr Camilla Whittington holding a Cunningham's skink.

    Dr Camilla Whittington from the School of Life and Environmental Sciences and Sydney Veterinary School at the University of Sydney.

    File size: 342.5 KB

    Attribution:

    Permission category: © - Only use with this story

    Last modified: 03 Apr 2019 10:20am

    NOTE: High resolution files can only be downloaded here by registered journalists who are logged in.

  • A three-toed skink (Saiphos equalis)
    A three-toed skink (Saiphos equalis)

    A three-toed skink (Saiphos equalis) baby hatching from an egg. NB: this is not the young discussed in the paper.

    File size: 5.5 MB

    Attribution: Nadav Pezaro from Haifa University

    Permission category: No right reserved (waive all rights)

    Last modified: 04 Apr 2019 12:05am

    NOTE: High resolution files can only be downloaded here by registered journalists who are logged in.

Show less
Show more

Media contact details for this story are only visible to registered journalists.